Multilayer interference pigment with transparent central layer

Abstract

Multilayer interference pigment consisting of a central layer of a transparent or semitransparent material of low refractive index and alternating layers of a metal or of a material of high refractive index and of a material of low refractive index either side of the central layer, the material of low refractive index preferably being magnesium fluoride or acrylate and the metal preferably being aluminium or chromium.

What is claimed is: 
     
       1. A multilayer interference pigment in the form of pigment particles consisting of a central layer of a transparent or semitransparent material of low refractive index and alternating layers of: (a) a metal or a material of high refractive index and   (b) a material of low refractive index, on either side of the central layer.   
     
     
       2. An interference pigment according to claim 1, wherein at least one material of low refractive index is MgF 2 , a metal oxide or a polymer. 
     
     
       3. An interference pigment according to claim 1, wherein at least one material of low refractive index is an acrylate polymer. 
     
     
       4. An interference pigment according to claim 1, wherein at least one material of low refractive index is an SiO 2  or Al 2  O 3  or a mixture thereof. 
     
     
       5. An interference pigment according to claim 1, having at least one layer of high refractive index being a metal layer of aluminum, chromium, nickel, a Ni--Cr alloy or silver. 
     
     
       6. An interference pigment according to claim 1, having at least one layer of a material of high refractive index being TiO 2 , ZrO 2 , Fe 2  O 3 , Cr 2  O 3 , ZnO or a mixture of these oxides or an iron titanate, a titanium suboxide or a mixture or mixed phase of these compounds. 
     
     
       7. A process for preparing an interference pigment according to claim 1, which comprises: applying a release layer comprising a water- or solvent-soluble material to a substrate,   depositing a layer system comprising the alternating layers of a material of low refractive index and of a metal or of a material of high refractive index onto the release layer, the central layer applied being a layer of a transparent or semitransparent material of low refractive index,   removing the layer system from the substrate by dissolving the release layer, and washing and drying the resulting platelet-shaped interference pigment,   subjecting the pigment to heat treatment at from 100 to 300° C., in a stream of nitrogen, and   milling and classifying the treated pigment.   
     
     
       8. The process of claim 7, wherein at least one material of low refractive index is MgF 2 , a metal oxide or a polymer. 
     
     
       9. A process according to claim 7, wherein at least one material of low refractive index is an acrylate polymer. 
     
     
       10. A process according to claim 7, wherein at least one material of low refractive index is SiO 2  or Al 2  O 3  or a mixture thereof. 
     
     
       11. A process according to claim 7, wherein at least one layer of high refractive index is an aluminum, chromium, nickel, a Ni--Cr alloy or silver metal layer. 
     
     
       12. A process according to claim 7, wherein at least one layer is of a material of high refractive index which is TiO 2 , ZrO 2 , Fe 2  O 3 , Cr 2  O 3 , ZnO or mixtures of these oxides or an iron titanate, titanium suboxide or a mixture of mixed phase of these compounds. 
     
     
       13. A paint, printing ink, plastic or cosmetic composition comprising a pigment according to claim 1. 
     
     
       14. A composition according to claim 13, wherein the pigment is provided in admixture with at least one other pigment. 
     
     
       15. A method for pigmenting a paint, printing ink, plastic or cosmetic which comprising mixing therewith a pigment according to claim 1.